Popular Science Monthly 



701 



The balancing-chamber is a small 

 metal bell with a tube at the top and a 

 small hole in the side near the bottom. 

 When the balancing-chamber is sunk, 

 liquid is forced into the hole, the re- 

 sultant pressure being transmitted 

 through the pipe to the mercury indi- 

 cator. The indicator resembles an old- 

 style barometer, having a tall mercury 

 column. As soon as the balancing- 

 chamber has been sunk to the bottom of 

 the tank the mercury- column will rise 

 no higher; it is then necessary to balance 

 the system by means of compressed air. 

 This is necessary to compensate for the 

 loss of pressure transmitted due to the 

 length of the copper tube. A valve at 

 the bottom of the indicator is turned so 

 that the balancing-chamber is in direct 

 communication with the .air-pump. A 

 few strokes of the pump force out the 

 liquid from the sunken chamber. Then 

 the valve is turned back to its former 

 position and the pressure is correctly 

 registered on the dial by the mercur>^ 

 column. The accompanying drawings 

 explain the system so clearly that 

 further elucidation is hardly necessary. 



With this device it is not only possible 

 to determine correctly the amount of 

 water or oil in the tank — and the cali- 

 bration of the gage can be easily trans- 

 lated into gallons — but it can be em- 

 ployed for determining the tonnage of a 

 vessel by the use of a balancing-chamber 

 in the bow and another in the stern. 

 Both of these chambers communicate 

 through tubing to twin dials located in a 

 convenient place. 



Two of the accompanying diagrams 

 illustrate the manner in which the ap- 



paratus is installed for determining a 

 ship's draft. A one-inch hole is bored 

 in the bow a few inches below the water 

 line when the vessel is. unloaded. If four 

 equipments are installed instead of two — 

 one on the port side and the other on the 

 starboard side in the bow and the other 

 two installed similarly in the stern, it is 

 an easy matter by having the four gages 

 side by side to tell whether the ship is 



The bell-like object is contained in a small 

 tank which communicates with a hole 

 below the water line in a ship's side. The 

 variations in water pressure are communi- 

 cated to the gage. The purpose of the air- 

 pump is to balance the system for accuracy 



As the vessel sinks in the water, due to natural or accidental causes, the increased pressure 



is transmitted through copper tubing to indicators in the cabin's office, the chart-room or 



the engine-room, giving due warning to the officers of the ship 



